title: Effects of temperature on the dynamics of the LacI-TetR-CI repressilator.
abstract: We studied the behaviour of the repressilator at 28 °C, 30 °C, 33 °C, and 37 °C. From the fluorescence in each cell over time, we determined the period of oscillations, the functionality (fraction of cells exhibiting oscillations) and the robustness (fraction of expected oscillations that occur) of this circuit. We show that the oscillatory dynamics differs with temperature. Functionality is maximized at 30 °C. Robustness decreases beyond 30 °C, as most cells exhibit 'failed' oscillations. These failures cause the distribution of periods to become bimodal, with an 'apparent period' that is minimal at 30 °C, while the true period decreases with increasing temperature. Based on previous studies, we hypothesized that the failures are due to a loss of functionality of one protein of the repressilator, CI. To test this, we studied the kinetics of a genetic switch, formed by the proteins CI and Cro, whose expression is controlled by PRM and PR, respectively. By probing the activity of PRM by in vivo detection of MS2-GFP tagged RNA, we find that, beyond 30 °C, the production of the CI-coding RNA changes from sub-Poissonian to super-Poissonian. Given this, we suggest that the decrease in efficiency of CI as a repressor with temperature hinders the robustness of the repressilator beyond 30 °C. We conclude that the repressilator is sensitive but not robust to temperature. Replacing CI for a less temperature-dependent protein should enhance robustness.
authors.affiliation: Computational Systems Biology Research Group, Tampere University of Technology, P.O. Box 553, 33101 Tampere, Finland. andre.ribeiro@tut.fi.
authors.forename: Jerome G
authors.initials: JG
authors.lastname: Chandraseelan
authors.forename: Samuel M D
authors.initials: SM
authors.lastname: Oliveira
authors.forename: Antti
authors.initials: A
authors.lastname: Häkkinen
authors.forename: Huy
authors.initials: H
authors.lastname: Tran
authors.forename: Ilya
authors.initials: I
authors.lastname: Potapov
authors.forename: Adrien
authors.initials: A
authors.lastname: Sala
authors.forename: Meenakshisundaram
authors.initials: M
authors.lastname: Kandhavelu
authors.forename: Andre S
authors.initials: AS
authors.lastname: Ribeiro
mesh_terms: D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000378:metabolism*; D049452:Green Fluorescent Proteins / Q000378:metabolism; D007700:Kinetics; D008954:Models, Biological; D012097:Repressor Proteins / Q000378:metabolism*; D013696:Temperature
chemical_list: D029968:Escherichia coli Proteins; D012097:Repressor Proteins; D049452:Green Fluorescent Proteins